Cheapie purple test

C

On the cheapie ones is it normal for the positive to get darker after the 3 mins is up? I know it says not to read after 10 but is that just for negative tests? mine have gotten darker as time goes on(15-20 moms later)

Is it just the dye setting in and drying?

First pic is 3 mins in and the second pic is about 20

Am i way over thinking this lol